Most tablets cost £1 or £2 each and were sold with claims that they would “boost brainpower” and “increase memory”.

Another drug claimed to boost concentration levels was Sunifiram, which has never been approved for use anywhere in the world, trialled in humans, or even subjected to basic safety tests.

Life in your hands

Harry Shapiro, founder of drug charity Druglink, warned: “You don’t know if a prescription drug bought online is suitable for you, or if it will react badly with something else you are taking.

“You’re taking your life in your hands, becoming a human guinea pig.”

Another tablet claiming to be Adderall, a treatment for Attention Deficit Hyperactivity Disorder, was found by lab testing to be potentially deadly painkiller Tramadol.

Similar to heroin in effect, Tramadol is highly addictive. As a Class C drug, possession is punishable by two years in jail and supply punishable with up to 14.

David New

Most pills cost a few quid and sold with claims that they would 'boost brainpower'

Dubbing The Sun’s findings “extremely concerning”, University of Cambridge neuroscientist Professor James Rowe said: “If users don’t know they’re taking it and consume other painkillers too, the chances of an overdose are even higher.

“There are similarly high risks if you unknowingly took these drugs with alcohol.”

All other tablets bought by The Sun were confirmed to contain the chemical they were claimed to, though not necessarily at the stated concentration, preventing users accurately judging their dose.

Despite their official-looking packaging, most pills are likely to be “copies” of brand-name tablets, usually made in China or India and some in unprofessional conditions.

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Over the past three years, Britain’s Medicines and Healthcare Regulatory Authority (MHRA) has seized around 93,000 doses of tablets claimed to boost brainpower and over the past year alone shut down nearly 5,000 UK-based websites selling substances including “smart drugs”.

However, most of the websites used by The Sun are based in India or China, meaning British authorities are powerless to act against them.

Wonder drug . . . Modafinil is licensed to treat narcolepsy

Research earlier this year by student newspaper group The Tab found study drugs were most popular at the University of Hull, where 37 per cent admitted taking them, while at both Newcastle University and the University of Sussex 31 per cent had used the pills.

The same survey found economics and engineering students were the most likely users, with 31 and 26 per cent of those admitting to taking smart drugs.

Former student Madeleine Grant, 24, took Modafinil while studying at the University of Oxford but it came at a price. She said: “I felt quite anxious and anti-social.

Jamie Lorriman

Student Madeleine Grant, 24, took Modafinil while studying at University

“And after a sleepless night on Modafinil, I’d often experience minor hallucinations.”

Smart drugs use is not confined to students. Research by the MHRA as part of their recent Fake Meds campaign has revealed 11 per cent of 18-30-year-olds — around 1,034,374 young people — have taken the drugs within the last year.

Professor Rowe said: “These smart drugs have a mild stimulant effect on the brain, making users feel more clear-headed and less tired.

“If you have a disorder like dementia, schizophrenia or ADHD, then a carefully monitored dose of these drugs can help restore a more ‘normal’ level of function.

There’s no way users can know what is in them

“If you have a healthy brain, it’s much less clear.

“Adderall can affect the heart which could be dangerous. Other drugs, are extremely addictive.

“Even more worrying, when tablets are bought online, there’s no way users can know what is actually in them.”

'I HAD HALLUCINATIONS'

MADELINE GRANT, 24, of Warwick, above, studied English at Oxford University and now works for a political think tank. She said:

I first took Modafinil in second year to get an essay done at the last minute.

My friend gave me a tablet, and I took it at 10pm – then worked feverishly until 6am when I sent my essay off.

It was like an electric light had gone off in my brain.

From then on I took Modafinil and pulled all-nighters almost every week but I experienced various side effects, some quite worrying.

I felt quite anxious and found it very difficult to sleep if I’d taken a whole pill.

I’d often experience minor hallucinations and even paranoia convinced there was someone in my room when there wasn’t, as well as an upset stomach.

These days I’ve stopped using them.

As I’ve got older, I’ve realised the side effects weren’t worth the boost in focus.

'SHAKING AND SCARED'

STUDENT Levi Rogers, 22, of Preston, took pills while studying Law at Queen Mary University in London. He said:

I took study drugs at university. I’d left my work to the last minute and a friend suggested that I try Modafinil.

I was given a tablet bought online and I took it before sitting down with my books.

I worked flat out for eight hours, totally focused on my essay. But I didn’t quite feel “right”. My mind was speeding at 100mph, leaping from one thought to another. I felt very jittery.

I kept moving around and checking my phone, though my hands were really shaky.

It was scary and very unpleasant.

Looking back, I can’t be sure of what they actually were.

I went on to use the drug around ten times, with the same effects each time.